Allow deployable ping URL composition

Description

Right now deployable ping URL in Maven plugin has to be set as whole URL.

This brings complications in case if I want to use port offset for starting several containers. For every Cargo execution I have to define separate deployable element with appropriate ping URL. This URL is also maintained separately - if I update servlet port I have to also update ping URL to new port.

Purpose of this improvement is to add possibility to define ping URL as just path part of URL.For example to have ping URL as http://localhost:8080/cargo would be enough to just set ping URL to /cargo .